1. Field of the Invention
The present invention relates to methods and structures for attaching a semiconductor chip or chip carrier to a substrate and, more particularly, to methods and structures for attaching a semiconductor chip or chip carrier to a substrate using solder ball technology.
2. Background and Related Art
In the fabrication of electronic devices as, for example, during ball attach or card attach, low melt C4 (controlled collapsed chip connection) solder balls on a chip carrier will reach their melting temperature and become liquid. Typically, for solder with a high tin content, the volume expansion associated with this phase change can range between 3 and 6%. If the C4 solder balls have been encapsulated prior to this volume change, as is typically the case, the volume expansion is constrained and the resulting pressure may result in the squeezing of this expanding volume of liquid into voids present in the surrounding underfill and its associated interfaces. This volume expansion of solder may also result in opening any weak interfaces, like underfill to chip passivation (for example polyimide) or underfill to solder mask interfaces. It is clear that the effect of such action could result in device failure.